As it is known, a steering damper damps down on oscillations that can occur on the steering system and be transmitted to a driving member such as a handlebar of a motorcycle. Specifically in the field of motorcycling, it is particularly critical when there are such oscillations, since they can give way to a phenomenon of instability also known as the wobble or shimmy effect. Such an effect, if not suitably dampened, can also be very dangerous for the rider since it can lead to riding difficulties and the loss of control of the motorcycle.
However, the damping action of the damper, when not strictly necessary, or rather in non-critical riding conditions (without wobble effect), can have some drawbacks; in particular the resistance to the steering rotation is generally increased (so called “hardness” of the steering block), leading to less comfortable riding and causing the rider to become tired sooner, thus also negatively affecting riding safety.
Again the steering damper increases the overall weight of the motorcycle, negatively affecting its performance and the ease of riding.
Still limiting the considerations to the field of motorcycling, which the present description specifically refers to, one solution of a steering damper that is technically simple and relatively widespread is the one that provides a linear damper that is arranged externally with respect to the steering head and operates tangentially between the handlebar and the frame.
Research has recently, however, started aiming at more functional and compact systems, of rotary nature, that are formed on the axis of the steering block or associated with it. Among these, focus has been put on systems of the magnetorheological type, or rather that use fluids that, in the presence of a magnetic field, are capable of instantaneously and reversibly changing their inner viscosity in a proportional manner with respect to the magnetic field itself. Such a property of magnetorheological fluids is thus exploited so as to dampen, as a function of the velocity of the motorcycle, the mutual rotation between two components at least one of which is in direct kinematic connection with the steering shaft of the motorcycle.
Steering dampers of a rotary nature and using magnetorheological fluids have therefore been proposed. Among these, some systems potentially aimed for use with motorcycles (that impose stricter weight constraints, reduction of bulk, ease of maintenance, manufacturing cost-effectiveness) are for example those described in documents US2010/0270773, JP2010167999, WO2005035349 and WO2005035349.
Such systems are not however satisfactory, both in terms of overall efficiency and for the fact that they foresee a relatively high number of components which increases the constructive complexity, exposes the device to higher risk of breaking and complicates maintenance and assembly/disassembly operation, in particular when maintenance operations indeed require dismounting and subsequently reassembling the front part of the motorcycle.
Again, Japanese patent JP2009287639 and U.S. Pat. No. 6,318,522 disclose rotational dampers that are connected to the frame of a vehicle through some kind of supports. The dampers and the frame thus remain two structurally separate elements, and therefore, considering the fundamental requirement to avoid mechanical interferences, the dampers have blades that mainly develop in the radial direction, thus being axially compact.